1. Field of the Invention
The present invention relates to a vibration wave driving apparatus which obtains driving force from vibration waves, such as ultrasonic waves.
2. Related Background Art
A vibration wave driving apparatus which obtains driving force in three degrees of freedom (3D direction) using vibration waves, such as ultrasonic waves, has been proposed. Japanese Patent Application Laid-Open No. 11-220891 discloses a vibration wave driving apparatus which can excite, in a Langevin type vibration element, in-plane expansion and contraction vibrations that displace in a longitudinal direction and two different types of out-of-plane bending vibrations that displace in a direction perpendicular to the longitudinal direction. When at least two of these three types of vibrations are excited and synthesized, the driven member can be translated or rotated in an arbitrary direction.
Although vibration wave driving apparatuses are required to be reduced in size and improved in function, the vibration wave driving apparatus disclosed in Japanese Patent Application Laid-Open No. 11-220891 is subject to constraints in terms of a reduction in size in the longitudinal direction because in-plane expansion and contraction vibrations that displace in the longitudinal direction of the vibration element must be generated. As the size in the longitudinal direction decreases, the frequency of in-plane expansion and contraction vibrations increases. For this reason, to decrease this frequency to a practical frequency, a certain size must be ensured in the longitudinal direction.
A vibration wave driving apparatus whose size in the longitudinal direction is reduced is disclosed in U.S. Pat. No. 5,917,268. This apparatus is designed to generate driving force in two degrees of freedom by exciting two types of in-plane expansion and contraction motions and natural modes of two types of out-of-plane bending vibrations in a planar type vibration element. More specifically, the driven member is translated or driven in the first direction by synthesizing a first in-plane expansion and contraction motion and third out-of-plane bending vibration. The driven member is translated or driven in the second direction by synthesizing second in-plane expansion and contraction motion and fourth out-of-plane vibration.
This vibration wave driving apparatus is, however, designed to generate driving force in two degrees of freedom, but there is no suggestion about an arrangement for generating driving force in three degrees of freedom. In addition, since two types of in-plane expansion and contraction motions must be generated, this apparatus is subject to constraints in terms of a reduction in size in the longitudinal direction of the plate in order to suppress the frequency of vibrations. Therefore, the technical idea of this apparatus differs from that of the present invention, i.e., obtaining driving force in three degrees of freedom and reducing the size in the longitudinal direction.
According to one aspect of this invention, there is provided a vibration wave driving apparatus which drives a driven member by vibrations excited in a vibration member having electro-mechanical energy conversion elements, wherein the vibration member has a shape line symmetrical with respect to two planes orthogonal to each other, and the electro-mechanical energy conversion elements can excite in the vibration member three different types of bending vibrations which displace in a direction of axis common to two planes.
This vibration wave driving apparatus can drive the driven member in an arbitrary direction in three dimensions by selectively exciting two of the three types of bending vibrations.
Since three types of bending vibrations that displace in the same direction are excited, the vibration member may have a plate-like shape and can be formed thin. In addition, since all the vibrations excited by the electromechanical energy conversion elements are bending vibrations, the natural vibration frequency can be suppressed low as compared with expansion and contraction vibrations. This makes it possible to reduce the size of the vibration wave driving apparatus.
Note that two of the three different types of bending vibrations have the same vibration pattern and are 90xc2x0 out of phase in the same plane.
The electromechanical energy conversion elements capable of exciting the three types of bending vibrations are preferably arranged in the same plane.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.